Can I still negotiate after verbally accepting an offer?

You accepted it in writing if you did it by email. However, if you did not get the offer letter yet, it is not yet a formal acceptance. When the offer arrives, if you open negotiations again, yo are in effect making a counter offer, which from a legal point of view means that you have rejected the written offer. At that point, the writer can withdraw it and either negotiate further or terminate negotiations. Opening negotiations after you receive the offer may leave you with no offer. Or the writer may say the offer still stands, which means your counter offer is rejected and you can either accept the offer or not. You could also send an email indicating that you wish to withdraw your premature acceptance of the offer pending receipt of the formal written offer so that you can study it in detail. Just remember that not accepting the offer may result in it being withdrawn.  more

it may delay your application plus might be the reason for them to think twice. if the difference is only a small amount of money or benefits, just accept their offer.  more